Java - database connection mode

Here are five ways to connect java to a database.

@Test

If you find it is red,  Alt + enter. 

Here I choose the JUnit 5.8.1.

Wait for a while.

 Then you can find the Test (org.junit.jupiter.api).

1.

@Test
    public static void main(String[] args) throws SQLException {
        Driver driver = new Driver();
        String url = "jdbc:mysql://localhost:3306/j_db01";

        //将 用户名和密码放入到Properties 对象
        Properties properties = new Properties();
        properties.setProperty("user", "root");
        properties.setProperty("password", "123456");

        Connection connect = driver.connect(url, properties);
        System.out.println(connect);
    }

2.

//方式2
    @Test
    public void connect02() throws ClassNotFoundException, InstantiationException, IllegalAccessException, SQLException {
        Class<?> aClass = Class.forName("com.mysql.cj.jdbc.Driver");
        Driver driver = (Driver) aClass.newInstance();

        String url = "jdbc:mysql://localhost:3306/j_db01";
        //将 用户名和密码放入到Properties 对象
        Properties properties = new Properties();
        properties.setProperty("user", "root");
        properties.setProperty("password", "123456");

        Connection connect = driver.connect(url, properties);
        System.out.println("方式2=" + connect);
    }

3.

//方式3 使用DriverManager 替代Driver
    @Test
    public void connect03() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
        Class<?> aClass = Class.forName("com.mysql.cj.jdbc.Driver");
        Driver driver = (Driver) aClass.newInstance();

        //创建url 和user 和password
        String url = "jdbc:mysql://localhost:3306/j_db01";
        String user = "root";
        String password = "123456";

        DriverManager.registerDriver(driver); //注册Driver驱动

        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println("第三种方式=" + connection);
    }

4.

//方式4：使用Class.forName 自动完成注册驱动，简化代码

    @Test
    public void connect04() throws ClassNotFoundException, SQLException {
        //使用反射加载了Driver类
        //在加载Driver类时，完成注册
        /*
        源码：1.静态代码块，在类加载时，会执行一次
        2.DriverManager.registerDriver(new Driver());
        3.因此注册driver的工作已经完成
        static {
            try {
                DriverManager.registerDriver(new Driver());
            } catch (SQLException var1) {
                throw new RuntimeException("Can't register driver!");
            }
        }
         */
        Class.forName("com.mysql.cj.jdbc.Driver");

        // 创建url 和user 和password
        String url = "jdbc:mysql://localhost:3306/j_db01";
        String user = "root";
        String password = "123456";
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println("第4种方式=" + connection);
    }

5.

//方式5，在方式4的基础上改进，增加配置文件，让连接mysql更加灵活
    @Test
    public void connect05() throws IOException, ClassNotFoundException, SQLException {
        //通过Properties对象获取配置文件的信息
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));

        //获取相关的值
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String driver = properties.getProperty("driver");
        String url = properties.getProperty("url");

//        Class.forName("com.mysql.cj.jdbc.Driver");
        Class.forName(driver);

        Connection connection = DriverManager.getConnection(url, user, password);

        System.out.println("方式5 " + connection);
    }

Here is all the java code:

package com.jdbc;

import com.mysql.cj.jdbc.Driver;
import org.junit.jupiter.api.Test;

import java.io.FileInputStream;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

/**
 * java 连接mysql 的五种方式
 */

public class JdbcConn {

    @Test
    public static void main(String[] args) throws SQLException {
        Driver driver = new Driver();
        String url = "jdbc:mysql://localhost:3306/j_db01";

        //将 用户名和密码放入到Properties 对象
        Properties properties = new Properties();
        properties.setProperty("user", "root");
        properties.setProperty("password", "123456");

        Connection connect = driver.connect(url, properties);
        System.out.println(connect);
    }

    //方式2
    @Test
    public void connect02() throws ClassNotFoundException, InstantiationException, IllegalAccessException, SQLException {
        Class<?> aClass = Class.forName("com.mysql.cj.jdbc.Driver");
        Driver driver = (Driver) aClass.newInstance();

        String url = "jdbc:mysql://localhost:3306/j_db01";
        //将 用户名和密码放入到Properties 对象
        Properties properties = new Properties();
        properties.setProperty("user", "root");
        properties.setProperty("password", "123456");

        Connection connect = driver.connect(url, properties);
        System.out.println("方式2=" + connect);
    }

    //方式3 使用DriverManager 替代Driver
    @Test
    public void connect03() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
        Class<?> aClass = Class.forName("com.mysql.cj.jdbc.Driver");
        Driver driver = (Driver) aClass.newInstance();

        //创建url 和user 和password
        String url = "jdbc:mysql://localhost:3306/j_db01";
        String user = "root";
        String password = "123456";

        DriverManager.registerDriver(driver); //注册Driver驱动

        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println("第三种方式=" + connection);
    }

    //方式4：使用Class.forName 自动完成注册驱动，简化代码
    //这种方式方式获取连接是使用的最多，推荐使用
    @Test
    public void connect04() throws ClassNotFoundException, SQLException {
        //使用反射加载了Driver类
        //在加载Driver类时，完成注册
        /*
        源码：1.静态代码块，在类加载时，会执行一次
        2.DriverManager.registerDriver(new Driver());
        3.因此注册driver的工作已经完成
        static {
            try {
                DriverManager.registerDriver(new Driver());
            } catch (SQLException var1) {
                throw new RuntimeException("Can't register driver!");
            }
        }
         */
        Class.forName("com.mysql.cj.jdbc.Driver");

        // 创建url 和user 和password
        String url = "jdbc:mysql://localhost:3306/j_db01";
        String user = "root";
        String password = "123456";
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println("第4种方式=" + connection);
    }

    //方式5，在方式4的基础上改进，增加配置文件，让连接mysql更加灵活
    @Test
    public void connect05() throws IOException, ClassNotFoundException, SQLException {
        //通过Properties对象获取配置文件的信息
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\mysql.properties"));

        //获取相关的值
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        String driver = properties.getProperty("driver");
        String url = properties.getProperty("url");

//        Class.forName("com.mysql.cj.jdbc.Driver");
        Class.forName(driver);

        Connection connection = DriverManager.getConnection(url, user, password);

        System.out.println("方式5 " + connection);
    }


}

mysql.properties

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